The present disclosure generally relates to roll forming, pattern rolling machines. More particularly, the present disclosure relates to a high precision thread rolling machine assembly having a gear reduction assembly disposed between a pair of bearing assemblies.
Cold forming of a thread, gear tooth or other pattern upon a cylindrical blank utilizing reciprocating, symmetrical dies represents known technology. Examples are found in U.S. Pat. Nos. 387,184; 3,793,866 and 4,712,410. Such machines have not significantly changed since their initial design starting in the late 1800's. All machines manufactured to date use oil film ways, a moving carrier die block and threaded adjustments to compensate for all variations in the blank material to be formed, the tooling that used for forming and the natural tolerance variation and drift in traditional oil film ways. All modern, high precision manufacturing equipment such as CNC machining equipment current use linear bearings. The use of linear bearings in roll forming for threaded fasteners and other shapes has not been adapted because the required manufacturing speed (approximately 300 parts per minute) is beyond the current performance of any known linear bearing manufacturer.
Machine screws with rolled threads are widely used in industry. They are typically formed using known flat die technology in existence for many years. The commonly used flat rolling dies include a stationary (short) die on a stationary platen and a reciprocating (long) die on a reciprocating slide arranged in face-to-face relation.
As known by one of skill in the art, the machine drive advances the moving reciprocating or moving carrier die block to create the thread form. Though reliable, these machines require experienced operators to setup and run. The thread rolling machines most commonly used today represent technology developed long ago, with heavy metal components subject to wear and often requiring expensive adjustments and repairs.
In particular, all conventional thread rolling machines use a linear motion guideway commonly referred to as a hydrostatic linear motion bearing, commonly referred to as an oil film way. The oil film of the hydrostatic bearing stands up to the high pressure, oscillating manufacturing method of thread rolling, but the moving carrier die block attached thereto is subject to movement variation due the hydrostatic bearing and wear.
In all other high precision manufacturing equipment where an oil film way was used in the past has been replaced with a rolling element linear motion bearing that decreases friction by using rolling contact via rolling elements (balls, roller, etc.) that are placed between two relatively moving objects to provide highly accurate positioning operation.
However, simple direct replacement of an oil film way on a conventional thread rolling machine with a rolling element linear motion bearing assembly will fail without addressing two substantial and significant obstacles. First, manufacturing speeds for conventional thread rolling machines require approximately 300 strokes per minute and rolling element linear motion bearings cannot safely or efficiently operate at this speed. Second, the machine drive of conventional thread rolling machines operates on a well-understood slider-crank principal to translate rotary movement to linear movement. The machine drive commonly includes a pitman arm having a proximal end connected to the moving reciprocating die and a distal end connected to a flywheel. Rotation of the flywheel moves the proximal end of the pitman arm and the moving reciprocating die connected thereto in a linear reciprocating movement. Consequently, unwanted off-angle and reaction forces act upon the moving, reciprocating die during roll forming operations. Unfortunately, rolling element linear motion bearings operate at their highest life capability when the rolling or oscillation force is directly in-line with the guide rail.
Therefore, there is a long felt but unresolved need in the art for a high precision thread rolling machine with a rolling element linear motion bearing assembly for the advantages that have been previously recognized and that overcome the disadvantages of the prior art and the obstacles to implementation.